Sen. Ed Markey (D-MA) said reports of missile cooperation between Riyadh and Beijing is "not surprising" and should spur congressional action.
In the early hours of Tuesday morning, North Korea fired off two ballistic missiles into the Sea of Japan, violating U.N. sanctions.
The discovery brings the number of China's known under-construction missile silos to about 250, according to research by the Federation of American Scientists.
Iran's ballistic missile program is a serious worry for the U.S. and its allies, and President Joe Biden's administration is facing pressure to roll the issue into nuclear talks.
The Missile Defense Agency this month awarded $277 million to L3Harris and Northrop Grumman as part of its Hypersonic and Ballistic Tracking Space Sensor project.
Joint Staff Surgeon Air Force Brigadier General Paul Friedrichs said it was "extraordinary" that no American soldiers were seriously injured in the January attack.
"It's not a stretch to say that Donald Trump's most lasting legacy may well be writing what he calls love letters to a dictator in North Korea," Joe Scarborough said.
Reports suggested the new submarine may have been designed to carry and launch ballistic missiles, which could in future be tipped with nuclear warheads.
Congresswoman and Democratic presidential candidate Tulsi Gabbard said her constituents in Hawaii are particularly concerned about North Korea's capabilities.
"Thus far what you've seen this president do is heap praise on Kim Jong Un and kind of revel in the spectacle of these summits, where nothing happens," said Ben Rhodes, former deputy national security adviser to Barack Obama.
At least 16 bases were continuing research.
"Contrary to our military's suspension of joint Korea-U.S. military exercises, North Korea is conducting military exercises on a scale similar to previous years."
On Wednesday, Saudi Arabia said it had intercepted another three Houthi ballistic missiles fired at its cities.
Japan approved a record-high defense budget for 2018 to face the threat from North Korea.
The head of Iran's Atomic Energy Organization warned of the country's capabilities amid mounting rhetoric between Tehran and Washington over the 2015 nuclear deal.
Brigadier General Hossein Salami said Trump could not back up his threats with military force.
The announcement of the new plans for Iran's navy come amid ratcheting tensions between Iran and the United States.
Seoul now has an "early capability" to defend against North Korea's nuclear missile threat.
Photos of the purported weapon were published a week after the U.N. imposed its harshest-ever sanctions on North Korea.